Illumination optical unit for EUV projection lithography, and optical system comprising such an illumination optical unit

Patent metadata

Field	Value
Publication number	US-9645501-B2
Application number	US-201414467418-A
Country	US
Kind code	B2
Filing date	Aug 25, 2014
Priority date	Mar 9, 2012
Publication date	May 9, 2017
Grant date	May 9, 2017

Abstract

An illumination optical unit for EUV projection lithography guides illumination light to an illumination field, in which a lithography mask can be arranged. A facet mirror with a plurality of facets guides the illumination light to the illumination field. Respectively one illumination channel which guides an illumination light partial beam is predetermined by one of the facets. Exactly one illumination channel is guided over respectively one of the facets. The illumination optical unit is configured so that, at any time and at any point in the illumination field when the illumination optical unit is in operation, any pairs of illumination light partial beams guided over different illumination channels are incident on this illumination field point at times of incidence, the time difference of which is greater than a coherence duration of the illumination light.

First claim

The invention claimed is:

1. An illumination optical unit configured to guide illumination light to an illumination field, the illumination optical unit comprising:
a first facet mirror comprising a plurality of first facets configured to guide the illumination light to the illumination field,
wherein during operation of the illumination optical unit:
the illumination light comprises a plurality of illumination light partial beams;
each illumination light partial beam is guided by a respective illumination channel;
each illumination channel is guided by a respective first facet;
no more than one illumination channel is guided by a given first facet;
the plurality of illumination light partial beams comprises a first illumination light partial beam and a second illumination light partial beam which is different from the first illumination light partial beam;
the first illumination light partial beam is guided to the illumination field by a first illumination light channel;
the second illumination light partial beam is guided to the illumination field by a second illumination light channel which is different from the first illumination light channel;
the first and second illumination light partial beams are incident simultaneously at the same point in the illumination field;
the first illumination light partial beam has a first travel time to the illumination field;
the second illumination light partial beam has a second travel time to the illumination field;
a difference between the first and second travel times is greater than a coherence duration of the illumination light; and
the illumination optical unit is an EUV illumination optical unit.

2. The illumination optical unit of claim 1 , further comprising a second facet mirror downstream of the first facet mirror in a beam path of the illumination light through the illumination optical unit, the second facet mirror comprising a plurality of second facets,
wherein during operation of the illumination optical unit:
each illumination channel is guided by a respective second facet;
no more than one illumination channel is guided by a given second facet.

3. The illumination optical unit of claim 2 , wherein:
the first facet mirror is a field facet mirror;
the first facets are field facets;
the second facet mirror is as pupil facet mirror;
the second facets are pupil facets;
the illumination optical unit comprises a transmission optical unit configured to superimpose imaging of the field facets in the illumination field; and
the transmission optical unit comprises the pupil facet mirror;
the illumination optical unit is arrangeable so that images of the illumination light source come to rest at the location of the pupil facets;
the pupil facet mirror is configured with a tilt so that the various illumination channels, by which each one of the field points of the illumination field is impinged upon by the illumination light partial beams during operation of the illumination optical unit, respectively have different illumination channel lengths between the light source and respectively one of the field points of the illumination field.

4. The illumination optical unit of claim 2 , wherein:
the first facet mirror is a field facet mirror;
the first facets are field facets;
the second facet mirror is embodied as pupil facet mirror;
the second facets are pupil facets;
the illumination optical unit comprises a transmission optical unit configured to superimpose imaging of the field facets in the illumination field;
the transmission optical unit comprises the pupil facet mirror;
the illumination optical unit is arrangeable so that images of the illumination light source come to rest at the location of the pupil facets;
a main mirror surface of the pupil facet mirror deviates from a plane reference surface so that the various illumination channels, by which each one of the field points of the illumination field are impinged upon by the illumination light partial during operation of the illumination optical unit, respectively have different illumination channel lengths between the light source and respectively one of the field points of the illumination field.

5. The illumination optical unit of claim 2 , wherein the illumination optical unit is configured so that during operation of the illumination optical unit:
travel time differences exist between the illumination light partial beams depending on differences in path lengths of beam paths of the illumination channels; and
between a location in the beam path of the illumination light prior to the division of the illumination light into the illumination light partial beams and the illumination field, each difference between the travel times of two different illumination light partial beams is always greater than a coherence duration of the illumination light for each location in the illumination field.

6. The illumination optical unit of claim 2 , further comprising an optical retardation component configured to divide at least one illumination light partial beam into a plurality of partial beam components,
wherein:
between a first location in the beam path of the illumination light and the illumination field, the partial beam components have such pairwise travel time differences amongst themselves that each difference between the travel times of the partial beam components of any illumination light partial beams is greater than the coherence duration of the illumination light; and
the first location lies both upstream of the division of the illumination light into the illumination light partial beams and upstream of the retardation component the partial beam components.

7. The illumination optical unit of claim 2 , further comprising a scanning device configured to scan an illumination beam over the first facets so that that the illumination light illuminates the illumination field during operation of the illumination optical unit,
wherein:
when incident on the first facet mirror, an entire beam crosssection of the illumination beam is greater than 20% of a reflection surface of one of the first facets; and
the scanning device is configured so that at any given time a given field point in the illumination field is illuminated via at most one of the first facets.

8. The illumination optical unit of claim 7 , wherein the scanning device is configured so that a scanning region extending over a plurality of first facets is scanned on the facet mirror during operation of the illumination optical unit.

9. The illumination optical unit of claim 2 , further comprising a scanning device configured to scan an illumination beam over the first facets so that the illumination light illuminates the illumination field during operation of the illumination optical unit,
wherein:
when incident on the first facet mirror, an entire beam crosssection of the illumination beam is greater than 200% of a reflection surface of one of the first facets; and
the scanning device is configured so that at any given time a given field point in the illumination field is illuminated only via first facets in which the optical path length difference of their corresponding illumination chancels differs by at least one coherence length.

10. The illumination optical unit of claim 2 , wherein the illumination optical unit is configured so that during operation of the illumination optical unit:
illumination channel pairs exist in which illumination light guided along the illumination channel pairs is incident at at least one point of the illumination field so that the time difference is less than a coherence duration of the illumination light; and
a cross-sectional area of at least one of the illumin

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Patra Michael
• Deguenther Markus

Classifications

• H05G2/0086

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